The present invention relates to the inspection of components using eddy current technology and, more particularly, to a device for inspecting a component having a complex geometric shape, such as a dovetail slot, gear tooth or the like of a gas turbine engine component or similar workpiece using a multiplicity of eddy current probe or circuit elements formed in an array.
Eddy current inspection is a commonly used technique for detecting discontinuities or flaws in the surface of components such as the components of a gas turbine engine. Eddy current techniques are based on the principle of electromagnetic induction in which eddy currents are induced within the component under inspection. The eddy currents are induced in the component by alternating magnetic fields created in a coil of an eddy current probe, referred to as a drive coil, when the probe is moved into proximity with the component under inspection. Changes in the flow of eddy currents are caused by the presence of a discontinuity or a crack in the test specimen. The altered eddy currents produce a secondary magnetic field which is received by the eddy current probe coil or by a separate sense coil in the eddy current probe which converts the altered secondary magnetic field to an electrical signal which may be recorded for analysis. An eddy current machine operator may then detect and size flaws by monitoring and analyzing the recorded signals.
One problem with inspecting the surface of a workpiece with an eddy current array is to maintain the array in conformance and/or contact with the surface, as the eddy current device or probe is scanned across the surface, and to cause each of the pluralities of drive and sense elements comprising the eddy current array to be maintained at their respective substantially constant distances from the inspection surface during scanning. Additionally, workpiece geometries may vary from one component to another because of manufacturing process variability. Variation in the distance between the drive and sense elements and the inspection surface or a gap between the probe and the inspection surface as the probe is scanned across the surface is referred to as liftoff and is undesirable.
Previous attempts have been made to create probes that are flexible enough to conform to the surface being inspected, for example by placing an eddy current probe having a soft rubber backing, a corrugated cover, and an eddy current array over an expandable bar device. A pneumatically-powered wedge apparatus is then used to force the eddy current array into intimate contact with the surface being inspected. Unfortunately, this probe construction is less than ideal and requires increased pneumatic pressure in order to force the probe to conform with the surface being inspected, which tends to wear out the probe rapidly.
Accordingly, there is a need for an eddy current array probe that can maintain an eddy current array in contact with a part feature without the application of excessive force.
The above-mentioned need is met by the present invention, which provides an eddy current array probe having a complaint body molded around a rigid insert. A flexible eddy current array circuit is wrapped around the outer surface of the compliant body.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.